Originally Posted by bxtorr19
I asked my nephew ( he manages the fish department in Petco) and he told me that heaters are not safe for any tank under 5 gallons and should only be used with a glass tank. They do have heaters taht are rated for smaller tanks but usually just leaving a lamp on should be enough to heat the water to the proper temp. Just get an external temp strip to ensure that the temp is correct.
I have a heater in my 4 gallon, but it came with the tank and works really well...